In recent years, from the viewpoint of global environmental problems, such as a problem of the exhaustion of energy resources and an increase in CO2 in the atmosphere, clean energy has been desired to be developed. Solar photovoltaic power generation using, in particular, solar cells out of semiconductor devices has been developed and put into practical use as a new energy source, and is now on the way to progress.
A double-sided electrode type solar cell has been a conventional mainstream solar cell, which includes for example a monocrystalline or polycrystalline silicon substrate having a light receiving surface having an impurity of a conduction type opposite to that of the silicon substrate diffused therein to provide a pn junction, and electrodes provided at the light receiving surface of the silicon substrate and a surface opposite to the light receiving surface, respectively. In the double-sided electrode type solar cell, it is also generally done to diffuse an impurity of the same conduction type as the silicon substrate in the silicon substrate at the back surface at a high concentration to provide high output by a back surface field effect.
Research and development have also been advanced also about back electrode type solar cells, in each of which an electrode is not formed on the light-receiving surface of a silicon substrate and is formed only on the back surface thereof (see, for example, Patent Literature 1 (Japanese Patent Laying-Open No. 2007-049079)).
Referring to schematic cross-sectional views in FIGS. 28(a) to 28(f), an example of a method for manufacturing a conventional back electrode type solar cell will be hereinafter described.
First, as shown in FIG. 28(a), after masking paste 102 is screen-printed on the entire surface of an n-type or p-type conductive semiconductor substrate 101 on the light receiving surface side and then dried, masking paste 102 is screen-printed on the surface of semiconductor substrate 101 on the back surface side so as to have an opening 114 partially provided therein.
Then, as shown in FIG. 28(b), an n-type dopant 104 is diffused through opening 114 in the back surface of semiconductor substrate 101, thereby forming an n-type dopant diffusion region 103.
Then, masking paste 102 of semiconductor substrate 101 on each of the light receiving surface side and the back surface side is entirely removed. As shown in FIG. 28(c), after masking paste 102 is again screen-printed on the entire surface of semiconductor substrate 101 on the light receiving surface side and then dried, masking paste 102 is screen-printed on the surface of semiconductor substrate 101 on the back surface side so as to have an opening 115 partially provided therein.
Then, as shown in FIG. 28(d), a p-type dopant 106 is diffused through opening 115 in the back surface of semiconductor substrate 101, thereby forming a p-type dopant diffusion region 105.
Then, as shown in FIG. 28(e), after a textured structure 108 is formed by texture-etching of the surface of semiconductor substrate 101 on the light receiving surface side, an antireflection film 109 is formed on textured structure 108 while a passivation film 107 is formed on the back surface side of semiconductor substrate 101.
Then, as shown in FIG. 28(f), after passivation film 107 on the back surface of semiconductor substrate 101 is provided with an opening through which each surface of n-type dopant diffusion region 103 and p-type dopant diffusion region 105 is exposed, an electrode for n type 112 and an electrode for p type 113 are formed that are in contact with n-type dopant diffusion region 103 and p-type dopant diffusion region 105, respectively. In this way, the conventional back electrode type solar cell is produced.